From a cost effectiveness point of view, the shipborne antenna is usually considered the most critical component in a shipborne terminal for maritime satellite communications (MARSAT). For possible use in such a system, a high gain autotrack antenna has been developed. The antenna utilizes a combined electronical and mechanical beam steering realized with two planar phased arrays mounted on a mechanical axis. The antenna system is designed for unmanned operation, utilizing an automatic search-and-track mode. After acquisition of a beacon signal from the satellite, a monopulse track mode keeps the antenna pointing position locked, to the direction of incident beacon signal, irrespective of the motions of the ship. Attention has been paid to multipath effects that may occur, in particular reflections from the surface of the sea. This paper is concerned with the design background and the development of the antenna system.